250 STUDIES IN IMMUNITY. 



casein, etc., may be produced in such a way. We have used 

 Hammarsten's method of obtaining horse fibrinogen.* 



The rabbits were given at intervals of 7 days 10, 12, 12 and 

 15 c.c. of this solution of fibrinogen and were bled 2 weeks after 

 the last injection. The serum, designated rabbit > fibrinogen 

 serum, 56 degrees, was tested with the pure fibrinogen. An abun- 

 dant precipitum is formed at once on mixing; no such precipitate 

 is formed with normal rabbit serum. We were further able to 

 determine by the method described that the rabbit > fibrinogen 

 serum fixes rabbit alexin in the presence of fibrinogen. In other 

 words, this immune serum contains a sensitizer for fibrinogen. 



From these facts we may conclude that rabbits injected with such 

 substances as milk, egg white, fibrinogen, and serum, form both 

 precipitins and sensitizers for the respective substances. The pro- 

 duction of sensitizers, then, is not dependent on the morphology of the 

 substance injected and the animal body mil react as well against amor- 

 phous material as against substances of definite histological structure. 



Just as the sensitizers of antimicrobial and hemolytic sera fix 

 the alexin of normal serum in presence of the corresponding antigen, 

 so do the sensitizers of sera active against amorphous organic pro- 

 ducts fix the alexin in presence of the substance in question. 



The majority of the immune sera we have worked with act on 

 complex mixtures like serum, milk and egg albumin. It would be 

 of interest to determine whether the sensitizer acts on the complex 

 as a whole or more particularly on one or several components of it. 



Several writers have considered this question in respect to coagu- 

 lins and with somewhat divergent results. It may be considered 

 proved, it seems to us, that the coagulin affects the globulins 



* Oxalated horse plasma (1 to 1000) is centrifugal ized and mixed with an equal 

 volume of 30 per cent solution of sodium chloride. The precipitate is redissolved 

 in 8 per cent salt solution and again precipitated with the 30 per cent solution; 

 after three or four successive precipitations the fibrinogen is redissolved in sterile 

 distilled water, as is possible owing to the sodium chloride carried down by the 

 precipitate. To test its purity the fibrinogen is mixed on the one hand with cal- 

 cium chloride and on the other with fresh blood serum. In the second mixture 

 coagulation occurs, proving there is fibrinogen present in solution. No coagu- 

 lation takes place in the first tube, showing that the proferment is absent. 

 We further determined by heat that no other albumins or globulins were 

 present. 



